This paper investigate how diagrams can be used as indices and queries in a case based functional design environment. Case bases for functional design need diagramming support for two reasons: First, most designers prefer to sketch early design ideas with a pen. They sketch diagrams to explore possible adaptations of old cases to current design tasks. Second, functional design tasks that deal with layout configuration such as arranging pipes and wires for building facilities often benefit from previous successful or failure cases. Therefore, we are developing an interactive tool called the Electronic Cocktail Napkin to enable designers to index, access, and adapt case knowledge for design using diagrams. The Napkin program has links to a case based design aid Archie to support reasoning with diagrams for case retrieval.